1. Field of the Invention
The present invention relates to a semiconductor light-receiving device.
2. Related Background Art
A photoelectric transducer such as photodiode (PD) and avalanche photodiode (APD) has conventionally been produced by forming a semiconductor layer with a pn junction onto a p- or n-type semiconductor substrate having a high concentration by crystal growth, impurity diffusion, or the like. Recently, from the viewpoints of high light-receiving sensitivity and high-speed response, a semiconductor light-receiving device in which an electrode including a bonding pad to be electrically connected to an electrode is disposed on a semi-insulating substrate has been developed and put into practical use.
For example, Japanese Patent Application Laid-Open No. SHO 63-285971 discloses a semiconductor light-receiving device in which two kinds of semiconductor layers having respective characteristics different from each other are exposed onto the same plane of a semi-insulating substrate, so that electrodes can be arranged on a flat face. Such a semiconductor light-receiving device is useful from the viewpoint of lowering capacitance; however, it necessitates a special technique of forming recesses in two stages with slightly different depths on the flat face of the semi-insulating substrate, and etching back a semiconductor layer laminated on the recesses and a material with a characteristic different from the semiconductor layer, such as photoresist, at substantially the same speed.
As a technique for ameliorating the problem mentioned above, a semiconductor light-receiving device having two kinds of semiconductor layers whose crystals are grown in a mesa structure on the flat face of a semi-insulating substrate, and electrodes disposed at exposed parts of the semiconductor layer has been disclosed. For example, Japanese Patent Application Laid-Open No. HEI 2-105584 discloses such a semiconductor light-receiving device as a conventional example.
However, the technique described in HEI 2-105584 produces a steep step with the height corresponding to the thicknesses of the semiconductor layers on the substrate, though neither shaping the substrate nor special etching technique is required. Forming the electrodes on such a step may not only cause disconnection and poor insulation, but also require a complicated, difficult manufacturing process. As a result, thus produced semiconductor light-receiving device may lower its yield and reproducibility, whereby its reliability as a product may decrease.